Process for the production of organo sulfur compounds



2,998,455 PROCESS FOR THE PRODUCTION OF ORGANO SULFUR COMPOUNDS Robert E. Leech, South Charleston, and James E. Knap,

Charleston, W. Va., assignors to Union Carbide Corporation, a corporation of New York No Drawing. Filed Mar. 11, 1960, Ser. No. 14,203

8 Claims. (Cl. 260-608) This invention relates to a novel method for preparing zlkyl organic sulfur compounds having from 2 to 30 :arbon atoms in the alkyl groups.

More specifically, the instant invention deals with a nethod of producing compounds such as alkylhydro- ;ulfides, alkyl sulfides, alkyl disulfides and alkyl poly- ;ulfides by reacting trialkyl aluminum compounds with elemental sulfur to form aluminum derivatives oftalkyl organo-sulfur compounds and then treating the aluminum derivatives with aqueous mineral acids. The alkyl organo-sulfur compounds can then be refined by conventional procedures.

In one modification of the above technique on alkyl sulfide is produced directly by reacting a trialkyl aluminum compound with an aluminum mercaptide of the formula:

where R is an alkyl group containing 2-30 carbon atoms. The present invention provides a convenient, efficient and economical method for the production of alkyl organic sulfur compounds. These compounds are well known in the art and have been used as accelerators in the manufacture of rubber, as short-stop agents and as lubricant and fuel additives. The mercaptans, which are prepared by the instant process, have additional uses as oxidation inhibitors in hair wavingpreparations, and in the preparation of detergents.

The preferred embodiment of this invention is the twostep process; namely, reacting a trialkyl aluminum with sulfur, and then treating-the reaction product with a mineral acid.

While not wishing to be boundby any theoretical considerations, it would appear that the reaction between the trialkyl aluminum and sulfur takes place in the following manner:

some of the aluminum thioalkyl then reacts with more trialkyl aluminum and more 'sulfur in 'the following manner:

and simultaneously, some of the aluminum thioalkyl reacts with more sulfur to yield complex aluminum polythioalkyl compounds containing many sulfur atoms. This reaction is illustrated in the following manner:

where x is an integer of from 2-100, preferably from 2-10.

It is pointed out that the above formula is not intended to represent a true chemical equation since the exact structure of the higher molecular weight aluminum polythiol alkyls is not accurately known. This formula is merely intended to illustrate that the sulfur further reacts with Al(SR) to produce higher molecular weight compounds.

As has been previously stated, the reaction mixture is then treated with an aqueous mineral acid to liberate the organic sulfur compounds. It would appear that this re- Patented Aug. 29,- 1961.

ice,

action can be illustrated by each of the following two equations:

The sulfur cmpounds may be purified by distillation and may also be interconverted with relative ease. For example, mercaptans can be oxidized to disulfides:

2RSH+1/20 RSSR+H O polysulfides can be pyrolyzed to disulfides:

and sulfides may be prepared from mercaptans and aldehydes at 2500 psi. and 175 C. under hydrogen:

H RomsH+nono -vuonlsormwmo Preparation of alkyl sulfur compounds via mercaptans is well known. in the art. Mercaptan synthesis and other known processes of producting alkyl sulfur compounds produce more than one specific type of sulfur compound. interconversion of sulfur products must be relied upon to increase the yield of the desired alkyl sulfur compound. In addition, prior known processes generally require more expensive raw materials such as alkyl halides, sulfates, and alcohols as a source of sulfur or as a source of the organic moiety. Many of these raw materials are not readily available nor as easily synthesized as the corresponding alkyl-aluminum compounds used in this in-. vention. V

Many methods of synthesizing aluminum alkyls arewell known. For the purposes of this invention, the alkylaluminum compound may be derived from any desired source which produces an aluminum alkyl with 2-30 carbon atoms per radical. Preparation of the starting aluminum alkyl does not form a necessary part of this invention. All aluminum alkyl bonds will react with sulfur to form alkyl sulfur compounds.

In the preferred embodiment of this invention any aluminum trialkyl or mixture of trialkyls obtainable by direct synthesis is reacted with elemental sulfur to form the aluminum derivative of the organo-sulfiur compound. Typical examples of such compounds are: triethylaluminum, tripropylaluminum, tributylaluminum, triisobutylaluminum, trihexylaluminum, trioctylaluminum, trinonylaluminum, tribenzylaluminum, tridodecylaluminum, and trieicosylaluminum.

The alkyl group on the aluminum need not be primary. Secondary alkylaluminum compounds can be used as a source of alkyl bonds. Branched alkyl compounds, such as tri(2-methylpentyl) and tri(2-ethylhexyl) can also be used as starting compounds in the preparation of alkyl sulfur compounds. From triethylaluminurn, long chain alkyls can be formed -by ethylene addition. Triethylaluminum can be reacted with ethylene to form trihexyl-, trioctyl-, tridodecyl-, etc. up to 30 carbon atoms by the method of Ziegler, Petroleum Refiner 34, 111-15 (1955). The products from such a growt reaction may not be uniform and may include alkyls of several molecular weights. When such an. alkyl mixture containing different carbon atoms is sulfurized in accordance with the present invention, the resulting sulfur derivalives will likewise be mixed in molecular weight. 1

A number of substituted alkylaluminum compounds can be sulfurized in accordance with the present process.

Both alkylaluminum halides and hydrides have been synthesized and can be used as the source of alkyl aluminum bonds.

Although examples herein given illustrate specific preparations prepared in accordance with this invention,

the versatility of the present process for the preparation of valuable organic sulfur compounds is made clear by the following description of the process including the process conditions required.

In the first step of this process elemental sulfur, generally in the solid state, is added to the desired aluminum alkyl, with or without a diluent, at an absolute pressure of to 100 atmospheres and at a temperature in the range of 20 to 300 C., with a preferred operating range of about 60 to about 150 C. Operating temperatures above about 120 C. can be used when it is desired to add molten sulfur to the aluminum alkyl for purposes of easier handling and metering. The time of reaction will be dependent on the particular aluminum alkyl employed as well as the temperature, pressure, and physical state of the sulfur. Generally about 0.1 to about hours, preferably from about 0.1 to about 4 hours, is sufficient to react all the sulfur. Although the process of sulfurization can be satisfactorily performed without a diluent, the resultant product is so viscous that it must be diluted prior to handling. It is therefore advisable to employ a diluent during the first step, such a diluent is preferably an aromatic hydrocarbon such as benzene or toluene. Any saturated hydrocarbon of the methane series or naphtenic hydrocarbons such as hexane, heptane, cyclohexane, and the like provide alternative satisfactory diluents. An oxygenated compound cannot be used as a diluent inasmuch as most oxygenated compounds react with alkyls. For example, ethers form a complex with alkylaluminum compounds which will not react with sulfur as readily as an uncomplexed alkyl. A reasonable amount of diluent used will range in the ratio of 0.5 to 40 volumes per volume of aluminum alkyl.

In the second step, the resultant product of the first step or sulfurization stage containing the aluminumorgano-sulfur compound of the desired alkyl sulfur compound or compounds is hydrolyzed to form the corresponding aluminum salt and liberate the organo-sulfur compound. Various acidic hydrolyzing techniques can be employed to eflect the desired result, the particular selection depending principally upon the composition of the sulfurization product mixture. Preferably the aluminumorgano-sulfur compound is treated with an aqueous mineral acid such as hydrochloric acid or sulfuric acid to effect hydrolysis with resultant formation of two layers-a lower aqueous layer and an upper organic layer. The lower aqueous layer is extracted with a diluent, and the extract is added to the upper organic layer. The extractant is preferably the same as the diluent used in the first step. The liberated sulfur compounds contained in the organic layer can be purified by distillation, for example and interconverted as illustrated previously.

The novelty of this invention does not reside solely in the means of treating the derivative of the organo-sulfur compound with aqueous mineral acid to liberate the organo-sulfur compound as various other means of hydrolyzing the alkyl sulfur compounds from the sulfurization stage product mixture will be apparent to those skilled in the art. Rather, the present invention embodies a novel, simple, and economical means of containing valuable organo-sulfur compounds by reacting an aluminum compound with sulfur to produce the aluminum derivative of the organo-sulfur compound and hydrolyzing the reaction mixture product to liberate the desired organo-sulfur compound. This invention is further illustrated by reference to the following examples which are illustrative only and should not be construed as limiting the invention which is properly defined in the appended claims.

EXAMPLE 1 Preparation of isobutyl-sulfur compounds In a 2-liter, 3-neck, Pyrex flask 50 grams of 99 percent triisobutylaluminum (0.25 mols) was diluted with 500 grams of toluene which had been dried over anhydrous magnesium sulfate. To the flask were attached a motordriven stirrer, a reflux condenser, a thermometer well, and a screwtype solids feed metering device. The feed hopper for the solids feeder was charged with 36.2 grams of sulfur (1.25 mols). The sulfur was added to the toluene solution, by means of the solids feeder, over a period of 25 minutes. During the addition the temperature rose from 27.5 to 41 C. The flask was heated for an hour until the sulfur had all reacted; the final temperature was 54 C. During the following hour and a quarter the reaction mixture cooled to 33 C. while being agitated under a nitrogen atmosphere.

The reaction product was transferred to a dropping funnel from whence it was added dropwise to 300 ml. of 6 percent sulfuric acid in a stirred flask. The addition took place over a period of 20 minutes during which the temperature rose from 27 to 57 C. The hydrolyzed product existed in two layers: a lower aqueous layer and an upper organic layer. The lower layer was extracted with 100-ml. of toluene, and the toluene extract was added to the upper layer. Analysis of this mixture showed the presence of 6.2 grams of isobutyl mercaptan, a yield of 9.3 percent based on the triisobutyl-aluminum.

The solution of sulfur compounds from this experiment was combined with those from two similar ones and distilled to isolate other isobutyl sulfur compounds. The contained isobutyl mercaptan was removed in the distillation fractions (SS-104 C.) boiling below toluene. From the mercaptan-containing material a 2,4-dinitrophenylthioether derivative was prepared by the procedure of Bost et al. [1. Am. Chem. Soc. 54, 1985 (1932)]. It melted at 76.5 C.; the reported melting point is 76 C. (R. L. Shriner and R. C. Fuson, Systematic Identificaw tion of Organic Compounds, third edition, John Wiley and Sons, New York, 1948), The next higher boiling fraction, toluene was removed and then three successive fractions collected were diisobutyl sulfide (thio ether), diisobutyl disulfide, and a mixture of disulfide-polysulfide. The boiling points and microanalytical analyses of these fractions are listed below.

After removal of the last fraction (still-kettle temperature 152 C. at 10 mm. Hg) the sulfur-containing residues began to decompose and the distillation was stopped. The weight ratio of compounds obtained in this manner was:

Compound: Parts by weight Isobutanethiol (isobutyl mercaptan) 1 Diisobutyl sulfide 0.36 Diisobutyl disulfide 1.23 Isobutyl polysulfides, ca 3.00

EXAMPLE 2 Preparation of J-octanethiol and other octyl-sulfur compounds In the reaction equipment described in Example 1, above, 48 grams (1.5 mol) of sulfur was added to 181.8 g. (0.40 mol) of percent trioctylaluminum. The addition took place with agitation over a period of 1 hour and 20 minutes, during which time the temperature was raised from 50 to 132 C., by the exothermic reaction and, by electrical heating. At the end of the reaction, the

product was so viscous that it was diluted with l-liter of benzene for handling. The benzene solution was hydrolyzed as detailed above using a solution of 60 grams of hydrochloric acid in a liter'of water. After hydrolysis, the water layer was extracted with benzene and that extract was combined with the original benzene layer. This combined solution was stripped of benzene and distilled through a 30 x 300-mm. packed column. A total of 37 grams of 1 octanethiol was recovered; this represents a yield of 20.8 percent, based on the trioctylaluminum. The purest fraction (87 percent) distilled between 63 C.

at a 6 mm. and 71 C. at 8 mm. of mercury. The octanethiol vapor pressure data in the literature, indicate respective boiling points of 64 and 70 C. at these pressures [Ellis, L. M. In, and Reid, E. E., J. Am. Chem. Soc. 54, 1674 (1932)]. From this fraction a 2,4-dinitrophenylthioether was made; the recrystallized derivative melted at 80.0-80.6" C. The literature value is 78 C. None of the higher molecular weight sulfur compounds was isolated, but their production was in the ratio of 1.45 parts per part of the mercaptan.

EXAMPLE 3 Reaction on sulfur with trioctddecylaluminum In the manner of the previous examples, 48 grams (1.5 mole) of sulfur was reacted with 392.2 gm. of a 73 per cent solution of trioctadecylaluminum (0.36 mols). Hydrolysis of a benzene solution of the product was again accomplished with an aqueous hydrochloric acid solution (6 percent). The lower layer was extracted with benzene, and the extract was added to the upper layer. The mixture when stripped of benzene was analyzed; it contained 36.3 grams of octadecanethiol, a yield of 11.6 percent.

Air oxidation of the mixture of sulfur-containing compounds caused the formation of a precipitate judge to be the octadecyl disulfide. Recrystallization of that precipitate gave crystals which melted at 61-61.5 C. The analysis of those crystals showed that they were not pure disulfide.

Calculated Found It is to be understood that the relatively low yields in the above examples can be markedly improved by operating under more severe conditions. More severe conditions would normally be employed in commercial opertion. Further, it is to be emphasized that the process of this invention may be readily carried out in a batch, semicontinuous, or continuous procedure without departing from the spirit or scope of the invention.

I claim:

1-. A method of preparing alkyl sulfur compounds which comprises reacting a trialkyl aluminum compound of the formula:

where R is an alkyl radical containing from 2-30 carbon atoms, with sulfur and recovering the refined alkyl sulfur compounds.

2. A method of preparing alkyl sulfur compounds which comprises reacting a compound of the formula:

AlR

where R is an alkyl group having 2 to 30 carbon atoms with sulfur at a temperature from 20 to 300 C. and at an absolute pressure of from 0 to 100 atmospheres, for a period of 0.1 to 10 hours to form aluminum organo sulfur compounds, hydrolyzing said aluminum organo sulfur compounds with an aqueous solution of a mineral acid and refining the liberated alkyl sulfur compounds.

3. The process of claim 2. wherein the temperature is from -150 C.

4. The process of claim 2 on which the process is carried out in the presence of an inert diluent selected from the class consisting of saturated, aromatic and naphthenic hydrocarbons.

5. The process of claim 2 wherein the mineral acids are selected from the class consisting of sulfuric and hydrochloric acids.

6. The process of claim 2 wherein the trialkyl aluminum is trioctylaluminum.

7. The process of claim 2 wherein the trialkyl aluminum is triisobutylaluminum.

8. The process of claim 2 wherein the trialkyl aluminum is trioctadecylaluminum.

No references cited. 

1. A METHOD OF PREPARING ALKYL SULFUR COMPOUNDS WHICH COMPRISES REACTING A TRIALKYL ALUMINUM COMPOUND OF THE FORMULA: 